An environmental problem characteristic of urban areas (Tokyo, Osaka, Nagoya, and other cities), known as the heat island phenomenon (a phenomenon in which the atmospheric temperature of an urban area is higher than in the suburbs with an islandlike form), is currently posing considerable problems with more hot nights, localized concentrated rainfalls, and other various such effects on the lives of urban residents.
To provide better countermeasures against the heat island phenomenon, the Japanese government has established the Ministerial Liaison Committee on Heat Island Countermeasures and has instituted a series of heat island countermeasures.
One of the series of countermeasures to the heat island phenomenon is to promote the greening on the site of private buildings etc., and on the rooftops of government facilities and the like. This is promoted by modifying fixed property taxes, providing subsidies, and the like. The objective is “to improve the covering of the earth's surface in order to prevent the reduction in evapotranspiration and the heating up of the earth's surface due to a reduction in green space and water surfaces, and a greater coverage of ground areas by buildings, pavements, and the like.”
On the other hand, one example of a method commonly implemented in order to introduce such greening countermeasures is to place planters that house suitable soil (light soil in the case of rooftops) on land sites and rooftops, and to cultivate plants in these planters. Also known is a method in which a plant cultivating apparatus (see Patent Document 1) capable of constant automatic water supply is used as a planter in which plants are grown.
Patent Document 1: Japanese Laid-open Patent Application No. 10-113081